to
form a zinc atom are left in the zinc plate. That makes the zinc
negative for it has more electrons than protons. The zinc ions take the
place of the positive ions which are already in the paste. The positive
ions which originally belonged with the paste, therefore, move along to
the carbon rod and there get some electrons. Taking electrons away from
the carbon leaves it with too many protons; that is, leaves it positive.
In the little flash light batteries, therefore, you will always find
that the round carbon rod, which sticks out of the center, is positive
and the zinc casing is negative.

The trouble with the battery like the one I used to make is that the
zinc plate wastes away. Every time a zinc ion leaves it that means that
the greater part of an atom is gone. Then when the two electrons which
were left behind get a chance to start along a copper wire toward the
positive plate of the battery there goes the rest of the atom. After a
while there is no more zinc plate. It is easy to see what has happened.
All the zinc has gone into solution or been "eaten away" as most people
say. Dry batteries, however, don't stop working because the zinc gets
used up, but because the active stuff in the paste, the ammonium
chloride, is changed into something else.

There's another kind of battery which you will need to use with your
radio set; that is the storage battery. Storage batteries can be used
over and over again if they are charged between times and will last for
a long time if properly cared for. Then too, they can give a large
current, that is, a big swift-moving stream of electrons. You will need
that when you wish to heat the filament of the audion in your receiving
set.

The English call our storage batteries by the name "accumulators." I
don't like that name at all, but I don't like our name for them nearly
as well as I do the name "reversible batteries." Nobody uses this last
name because it's too late to change. Nevertheless a storage battery is
reversible, for it will work either way at an instant's notice.

A storage battery is something like a boy's wagon on a hill side. It
will run down hill but it can be pushed up again for another descent.
You can use it to send a stream of electrons through a wire from its
negative plate to its positive plate. Then if you connect these plates
to some other battery or to a generator, (that is, a dynamo) you can
make a stream of electrons go in the other direction. Wh